#include<bits/stdc++.h>
using namespace std;
int a=0,b,c=1;
void pd(){
	if(b%2==0&&c*c%b<b/2) a++;
	if(b%2==1&&c*c%b<=b/2) a++;
	c++;
	return;
}
int main(){
	cin>>b;
	for(int i=1;i<b;i++) pd();
	cout<<a;
	return 0;
}